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Soils Lab
What is soil?
What is soil? Soil is material that covers the earth's surface. Soil is important because
without it plants would not grow which would not only cut off our food supply but would
create a lack of oxygen in the biosphere. Wind, rain, sun, chemicals, and other manmade
compounds often alter soil's physical and chemical properties. There are many layers of
soil, each differing in their organic composition and texture. During this lab you will
study samples of soil and assess their properties. There are nearly 21,000 soil types
found in the United States. There are three particle sizes that make up these soil types--silt,
clay and sand. Therefore, soil can be categorized into clayey, silty, or sandy soils. Soils can
vary greatly in color as well. The varieties in soil color are primarily influenced by the
percentage of minerals, organic matter, and elements found in the soil.
Why Soils are Important:
Many people live their entire lives without ever thinking about soil. Most think of it as
"dirt," a brown, messy substance which makes clothes and hands dirty. To many it may not
be important, but to others it is a crucial part of their lives. Many farmers depend on soil to
provide the nutrients their crops require. Housing developers and engineers look at the soil
before advancing their building plans because the soil structure has a significant role in the
stability of their designs. Have you ever seen a house with a sagging roof or with
cracks in the foundation? Although these damaging effects may be due to earthquakes or
other natural disasters, they may also be due to unstable soil, which can easily shift, crack,
swell, shrink, or even sink over time.
The Different Uses of Soil:
Each type of soil has a specific use. Some soils are great for supporting massive weight, like
the soil found under skyscrapers or other large buildings. Other types of soil are suitable
for farming, such as the clayey compositions used for rice or the silty compositions used for
strawberries, potatoes, and many other plants. Other types of soil are good for forests and
wildlife habitats. During this lab, you will learn how to determine the identification and the
capabilities of your soil sample by assessing its structure, texture, color and chemical
composition.
Clay, Sand, and Silt:
There are many different types of soil. Often a percentage of all three types of soil can be
found in a sample. The main types of soil focused on in this lab are stony soil (soil that
contains mostly rocks), sandy soil (soil that contains mostly sand), clay soil (soil that
contains fine particles, and is heavy, cool, and damp), loam (soil that contains sand and
clay), and peat soil (soil that contains decayed plants).
The different types of soil can primarily be tested by its texture and particle size. Clay is
smooth to the touch, heavy, and very thick. Soil samples with clay are comparable to
modeling clay. Silt resembles the traditional view of what dirt is. It is lighter and
resembles silly putty when wet. Sand, familiar to all, is what can be found on a beach.
Sand is manipulated much more easily than silt and especially clay.
Soil Characteristics
Characteristic
Color: Depends on the amount of air, water, organic
matter and certain elements.
Description
Brown to black: accumulation of organic matter,
humus
Purplish-black: accumulation of manganese
Yellow to reddish: accumulation of iron
Texture: Determines how well water drains from a
soil. Sand promotes drainage better than clay
White to gray: accumulation of salt
Sandy: feels rough
Silt: feels soft, silky or floury
Structure: The arrangement of smaller soil particles
to form larger pieces.
Clay: smooth when dry and sticky when wet
Granular: Individual particles of sand, silt and clay
grouped together in small, round grains.
Blocky: Soil particles cling together in block shapes.
Prismatic: soil particles have formed into vertical
pillars.
Chemical Composition: Influences what grows and
lives in the soil.
Platy: Soil particles form thin sheets piled
horizontally on one another.
Soil is measured by pH values of 1-14:
Neutral: pH of 7
Acidic: pH below 7
Alkaline (basic): pH above 7
OBJECTIVE: To examine soil samples and determine characteristic properties about each.
MATERIALS:
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Soil samples
Small dishes for soil
Pipettes/Eyedroppers
pH indicator paper
H2O
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Graduated cylinder
cup
plastic container for pH test
spoon
pH chart
PROCEDURE:
1. Get a scoop of soil from samples 1, 2 and 3. Place in your dish. Bring them back to
your table.
2. Follow the directions for each test below.
Test 1- Soil Color: Examine the soil samples and record their color in the data table. Use
the table on the first page of the lab to help you.
Test 2- Soil Texture: Rub each soil sample between your fingers. Don’t freak out! You can
wash your hands when you are done! Identify the texture and record the data in the data
table.
Test 3- Soil Structure: Examine the soil samples and determine the particle size and what
type of particles they are. Use the table on the first page of the lab to help you.
Test 4- pH:
1. Get a piece of pH indicator paper from your kit. Place one spoon full of soil in the
center cup of the plastic container, and add water from the cup, using the pipette,
until the soil is saturated.
2. Add 5 more drops of water and let sit for 30 seconds.
3. Carefully tilt the plastic container so that the excess runs into one of the small tubes
near the edge of the container.
4. DIP the piece of the pH paper into the excess water.
5. Quickly compare it to the colors on the chart in your kit.
6. Record the number that corresponds to the color on your test strip in the data table.
7. State if it is acidic, neutral or basic.
Test 5- Water-Holding Capacity:Using a pencil, punch a small hole in the bottom of a cup.
Add your soil sample. Hold the cup over a beaker. Add 100 ml of water to the graduated
cylinder. Pour the water over the top of the soil. Record the amount of time it takes the
water to collect in the beaker.
Soil Test
Color
Depends on the amount of
air, water, organic
material, and certain
elements in the soil
Texture (sand, silt, or
clay) Is it smooth?
Rough? Grainy?
Squishy?
Determines how well
water drains from a soil.
Sand promotes drainage
better than clays
Structure (Particle
Size: small, medium,
or large)
pH (# on scale and
acidic, basic or
neutral)
Influences what grows
and lives in the soil
Water- Holding
Capacity
Sample 1
Sample 2
Sample 3
Conclusion Questions
1. What can you conclude about the type of area these soils came from?
2. What can you conclude about all of the samples water holding capacity? Was the
water quick to drain or slow to drain for each sample?
3. What types of plants will grow well in acidic soil?
4. Compare the results of your pH test for all three samples.
5. What would happen to the flora and fauna (just a scientific way of saying plants and
animals) of an area if the pH changed drastically?